Goi=
ng to the future is a =E2=80=98done deal,=E2=80=99 but lots of problems wit=
h travelling to the past

By Mark Lowey

September 23, 2013

Paul Davies is a professor of physics at Arizona State University, an=
d the author of such titles as The Eerie Silence: Renewing our Search=
for Alien Intelligence, Quantum Aspects of Life, and How to Build=
a Time Machine. Photo by Dave Brown

However, travellers to the future won=E2=80=99t be able to return to the=
ir own time given the known laws of physics, he told an audience of more th=
an 700 at the University of Calgary, in a talk and slide show presented las=
t Friday by the university=E2=80=99s new Institute for Quantum Science and Techno=
logy.

=E2=80=9CThis is a one-way journey only,=E2=80=9D Davies said in an enga=
ging science presentation leavened with humour.

What is uncertain in the future is =E2=80=9Cwhether Calgary taxi drivers=
will have finally figured out how to navigate the campus,=E2=80=9D joked=
the professor of physics at Arizona State University.

Just a decade after H.G. Wells=E2=80=99s science fiction book, The Time=
Machine, was published in 1895, physicist Albert Einstein published his th=
eory of relativity in a 1905 paper which showed that time is =E2=80=9Celast=
ic=E2=80=9D and that time travel =E2=80=9Cis indeed possible,=E2=80=9D Davi=
es said.

=E2=80=9CTime can be stretched or warped,=E2=80=9D and the faster you mo=
ve, the more you warp time, he said, adding that =E2=80=9Ctime moves faster=
in space.=E2=80=9D

It would take a person travelling at nearly the speed of light (300,000=
kilometres per second) two years to get to the nearest star outside our so=
lar system, he said. But for a person on Earth, 20 years would have passed.=

=E2=80=9CThere is no absolute universal time. There is only relative tim=
e,=E2=80=9D Davies noted.

The force of gravity also influences time and warps space, including on=
Earth, he said.

Measurements by highly precise atomic clocks have shown that =E2=80=9Cti=
me runs a little bit faster on the roof than in the basement=E2=80=9D of a=
building.

Global positioning systems, which depend on a network of orbiting satell=
ites, have to account for such =E2=80=9Crelativistic=E2=80=9D time differen=
ces in order to be accurate.

If a person were able to go to the surface of a typical neutron star =E2=
=80=93 about the size of Calgary but with very dense mass and enormous grav=
itation force =E2=80=93 a clock would tick out only 70 per cent of the time=
compared with a clock on Earth.

On the surface of a black hole, which Davies called the =E2=80=9Cultimat=
e time warp=E2=80=9D because it is so dense that light can=E2=80=99t escape=
, time would stand still relative to time on Earth.

Although travelling to the future is possible, travelling to the past is=
filled with paradoxes that challenge what is currently known about physics=
, Davies said.

It might be possible to travel to the past through =E2=80=9Cwormholes,=
=E2=80=9D if these theoretical structures actually exist in the expanding,=
three-dimensional universe, or you could buy one from a =E2=80=9Cfriendly=
alien,=E2=80=9D he said.

Wormholes, whose existence is possible under Einstein=E2=80=99s theory=
of relativity, are =E2=80=9Cshortcuts=E2=80=9D that connect two different=
parts of space-time.

However, the immense gravitational field in wormholes would cause =E2=80=
=9Cspaghettification=E2=80=9D =E2=80=93 tearing to shreds a person travelli=
ng through them, Davies said. =E2=80=9CIt=E2=80=99s not something you would=
do lightly.=E2=80=9D

One of several paradoxes Davies cited is a man who goes to the past and=
shoots a young woman =E2=80=93 his mother. How could the son have been bor=
n if he killed his mother?

Such a =E2=80=9Ccausal narrative=E2=80=9D would only be possible if ther=
e are, as some scientists theorize, multiple universes with parallel realit=
ies, he said. Even if a son time-travels to the past and kills his mother=
in a parallel universe, in another universe the mother lives and the son=
is born.

So if all time is relative, what is time, really?

One answer, Davies offered with a smile: =E2=80=9CTime is nature=E2=80=
=99s way of preventing everything happening at once.=E2=80=9D

The serious side of Davies=E2=80=99 and other theoretical physicists=E2=
=80=99 work, including at the university=E2=80=99s Institute for Quantum Sc=
ience and Technology, is to understand the causal structure of space-time,=
to unify the theories of quantum physics and astrophysics.

The new institute, launched last week, is the only one of its kind in we=
stern Canada and the third of its scope in Canada.